Exploring The Hip Joint
Although most people are familiar with the general location of the hip joint, the network of bones, muscles, and ligaments that support their function is actually quite complex. These two joints have to mediate between our legs’ ability to adapt to the ground below and the response of our pelvis to what’s happening with our torso above.
To complicate things further, our right and left hip joints have to work together to coordinate our movement. Healthy mobile and stable joints are essential to our functional gait. During each step we take, our two hip joints function independently, but still in coordination with each other. When we walk we transfer our weight to one leg, while swinging our other leg forward to take a step. These joints are involved in every part of that process. That’s a lot to ask of our hip joints! In this article, we’ll explore the structures that make up these joints and how they all work together to support movement.
The hip joint
The hip joint is where the top of our leg meets our pelvis. We have two hip joints, of course, a right side and a left side.
What structures make up the hip joint?
Bones
On each of the right and left sides of the body, we have two bony connections that come together to create the hip joint. The top of the femur, which is the long bone of your thigh, ends in a knobby bit, called the head of the femur. That is the ball of the ball and socket joint. The femoral head fits into a depression in your pelvis, called the acetabulum. The acetabulum is the socket of the ball and socket joint. As you might guess, if you put the names of the two structures together, the technical name of the joint is the acetabulofemoral joint.
Joint type
The joint type of the hip joint is a ball and socket synovial joint. One of the hallmarks of a ball and socket joint is the ability of the joint to move in all planes. So, the hip is considered a multiaxial joint. It can move, not only in all three cardinal planes, but in many directions in between them too.
The multiplanar movement of the hip joint supports its function as a key joint in the lower body kinetic chain, all of which help us adapt to the changing nature of the ground under our feet. Its stability and the support of the strong musculature make this joint ideal for its function in weight-bearing and force transmission.
Ligaments
The hip joint is one of only two ball and socket-type joints in the body. The other ball and socket joint is your shoulder joint. In contrast to your shoulder joint, however, your hip joint is an incredibly stable joint. One reason for this is the depth of the hip socket that the head of your femur fits within. Another reason for the strength of this joint is the thick, dense ligaments that bind the pelvis to the femur. Three ligaments help maintain the stability of the joint. Those ligaments are the iliofemoral ligament, the pubofemoral ligament on the anterior side, and the ischiofemoral ligament on the posterior side.
Labrum
There is another structure that’s key to maintaining the integrity of each hip joint. Like the shoulder ball and socket joint, the hip joint is lined with an additional piece of cartilage called a labrum to help manage the balance of mobility and stability of the hip.
Muscles that cross the hip joint
Remember that muscles can contract to create movement, resist movement, and work to stabilize joints. When it comes to the muscles of the hip joint (and many other muscles too), most of the muscles can contribute to more than one action. In the next section where we list the muscles by their action, you’ll see that they appear in more than one list.
The muscles that cross the hip joint include:
- Rectus femoris
- Psoas major
- Iliacus
- Pectineus
- Adductor brevis
- Adductor longus
- Gracilis
- Adductor magnus
- Biceps femoris (long head)
- Semimembranosus
- Semitendinosus
- Sartorius
- Gluteus maximus
- Gluteus medius
- Gluteus minimus
- Tensor fascia latae
- Obturator internus
- Obturator externus
- Piriformis
- Quadratus femoris
- Gemellus superior
- Gemellus inferior
Movements at the hip joint
The main movements at our hip joint are:
- Flexion
- Extension
- Abduction
- Adduction
- Internal/medial rotation
- External/lateral rotation
- Circumduction
However, it’s important to remember here that our bodies are complex and three-dimensional. Because the hip joint does tri-planar movement, as well as many movements like circumduction that are in addition to moving along the lines of the three cardinal planes, we need to think of movement at the hip joint more broadly than at other joints with a more limited scope of movements.
Controversy at the hip joint
Most main actions at the hip joint involve certain muscles whose primary job is to create that action. However, many other muscles may assist with each action. Exactly which muscles contribute to which movements depends on the starting position of the hip joint during the movement. If we change the position of the joint from anatomical position to flexed past 90 degrees, for example, the physics of how the muscles around the joint work on and adapt to forces on the joint also change.
The variety of ways that some muscles assist particular movements at the hip joint are not fully understood by anatomists because the actions of many deeper muscles are hard to measure in a laboratory setting. There is some debate among researchers over the possible muscular contributions to movements at this joint. So, understand that although we list muscles and their associated movements below, researchers are still learning about the kinesiology of the hip joint. For that reason, you may see differences between references regarding which muscles assist which actions.
Flexion
Depending on the position of the hip joint, these muscles contribute to flexion:
- Rectus femoris
- Iliacus
- Psoas major
- Tensor fascia latae
- Pectineus
- Adductor brevis
- Adductor longus
Sartorius, gracilis, and the anterior fibers of gluteus minimus and medius may assist with hip flexion in some situations.
Extension
These muscles can contribute to extension:
- Gluteus maximus
- Adductor magnus
- Biceps femoris (long head)
- Semimembranosus
- Semitendinosus
The posterior fibers of the gluteus minimus and medius as well as the deep six lateral rotators acting bilaterally can potentially assist with hip extension in some circumstances.
Abduction
These muscles can contribute to abduction at the hip joint:
Under certain circumstances, piriformis and sartorius may assist with abduction of the hip.
Adduction
These muscles can contribute to adduction at the hip joint:
- Pectineus
- Adductor brevis
- Adductor longus
- Gracilis
- Adductor magnus
In some situations gluteus maximus, quadratus femoris, obturator internus, and biceps femoris can also contribute to adduction.
Lateral rotation
These muscles can contribute to external (lateral) rotation:
- Obturator internus
- Obturator externus
- Piriformis
- Quadratus femoris
- Gemellus superior
- Gemellus inferior
- Gluteus maximus
- Posterior fibers of gluteus medius and minimus
In particular situations, the sartorius can also assist with lateral rotation.
Medial rotation
These muscles can contribute to internal (medial) rotation:
- Tensor fascia latae
- Anterior fibers of gluteus medius and minimus
Medial, or internal rotation at the hip joint, is an interesting action because we don’t have a muscle or muscles whose primary action is internal rotation. Instead, we have smaller muscles that work together to create internal rotation. Depending on the position of the hip joint, it’s possible for adductor longus, adductor brevis, pectineus, and piriformis to assist with the action of internal rotation.
Conclusion
The hip joints might be among the joints in the body that people are most familiar with. However, their complexity is often far beyond what most people imagine. They are a crucial part of transferring force from the ground into the torso and from the upper body into the legs. The hip joints work with other key structures to make it possible for us to stand, walk, run, and do just about any other functional movement.
References
Chaitow, L. and J. DeLany. 2011. Chapter 12: The Hip. In Clinical Application of Neuromuscular Techniques. Volume 2 – The Lower Body (Second Edition). New York, NY: Churchill Livingstone Publishing.